The Celtics also secured their first sub-.500 season since 2006-07 (24-58).

Even if they win their remaining 18 games, they will finish with a record of 40-42.

But the Celtics were rather upbeat Tuesday, because they gave themselves a shot.

“This was a winnable game for us,” said Jeff Green, who shot 3 of 16. “We were right there. We were right there.”

After trailing by as much as 15, the Celtics cut the Pacers’ lead to 77-76 on a layup by Jared Sullinger with 6:44 left in the fourth quarter.

The Pacers responded with a 6-0 run, and the Celtics didn’t challenge again.

“We fought pretty hard,” said Rajon Rondo, who had 8 points and eight assists in a season-high 41 minutes. “I think we ran out of gas.”

Rondo, the Celtics’ captain and point guard, also felt like he could have done more after shooting 4 of 15 from the floor.

“I wasn’t as effective as I wanted to be,” he said. “I think I still could’ve dominated the game better. I’ve got to take this on myself as far as a loss.

“I could’ve done a lot more intangibles out there. I tried to get to the [free-throw] line; I came up short. But like I said, give my teammates a lot of credit. We fought tonight, but we didn’t get the victory.”

Stevens remained optimistic.

“We’re getting better, there’s no doubt about it,” he said. “Obviously you’ve got that great balancing thing of, our record is not very good, but especially in the last couple of weeks, with the exception of the Golden State game, I think we’ve done some good things at times.”

Rondo can also see strides.

“Yeah, I think even tonight, we didn’t make shots, but we still played better defense,” Rondo said. “Usually when we don’t make shots, we put our heads down and give up 100-plus points. But tonight, we kept fighting. We got stops when we needed to. We made a short run, but we just didn’t have enough.”

Bynum gave the Pacers a boost in his first game since Dec. 26, when he played with Cleveland. He scored 4 points and grabbed FIVE rebounds in his first four minutes on the court.

“Bynum came in and kind of changed the game for them a little bit,” said Humphries, “but I don’t think Hibbert did very much.”

Hibbert had 6 points and nine rebounds in 32 minutes.

Bynum, however, finished with 8 points and 10 rebounds in 15 minutes.

“I couldn’t do anything wrong today,” Bynum said.

David West led the Pacers with 24 points. Paul George scored a quiet 12.

For the Celtics, it boiled down to missed shots — and they were 3 of 19 from 3-point range.